1. Field of the Invention
The present invention relates to an exhaust gas purification device of an internal combustion engine having a structure for injecting an additive to be supplied to a catalyst.
2. Description of the Prior Art
For purification of an exhaust gas of a diesel engine vehicle (vehicle), in order to prevent emission of NOx (nitrogen oxides) and PM (particulate matter) contained in exhaust gas of a diesel engine into the air, an exhaust gas purification device in which NOx trap catalyst, selective reduction NOx catalyst, diesel particulate filter and the like are combined is used.
In this type of an exhaust gas purification device, such a structure is employed that in an exhaust passage for exhausting an exhaust gas exhausted from an engine to the outside, an oxidation catalyst, a NOx trap catalyst, a selective reduction NOx catalyst and the like called pre-stage catalyst is provided, and on an upstream side of the catalyst or an upstream side of the oxidation catalyst, for example, a fuel addition valve (to add a reducing agent) for injecting a fuel as an additive required for reaction of the catalyst is provided.
In order to have the fuel addition valve function normally all the time, it is required to avoid use of the fuel addition valve exceeding a heat-resistant temperature or generation of deposit at a distal end portion of the fuel addition valve causing clogging of injection.
Therefore, it is effective to keep the fuel addition valve away from an exhaust gas flow so as not to have the distal end portion injecting the fuel exposed to a high-temperature exhaust gas. An exhaust gas purification device disclosed in Japanese Patent Laid Open No. 2004-44483 is configured such that a fuel injection path branched from the exhaust passage and extended is provided at the exhaust passage and the fuel addition valve is installed at a distal end portion of the fuel injection path so that the fuel of the fuel addition valve is injected from a point far from the exhaust gas into the exhaust passage through the fuel injection path.
Since in such a structure that the fuel is injected from a point far from the exhaust gas flow, the fuel injection path is retreated from the exhaust passage, a flow of the exhaust gas flowing through the exhaust passage is hard to reach the inside of the fuel injection path. That is, since a stagnated portion easily occurs in the fuel injection path, the fuel evaporated in the fuel injection path can easily collect in the fuel injection path.
The evaporated fuel accumulated in the fuel injection path becomes a binder to have soot contained in the exhaust gas adhere to a wall surface of the fuel injection path and generate a deposit. Since the deposit is accumulated on the wall surface of the fuel injection path every time the fuel is injected, there is a possibility that the fuel injection path is blocked by the accumulated deposit.